My parents watch it, so I've had a fair few doses of their output from being at their house over the years. You're right that they do have many interesting talking points and raise some genuinely important issues from time to time which don't necessarily get much airtime elsewhere, it was actually a surprising revelation to me that they do have some value as an organisation. Unfortunately, for all the interesting talking points they have, it's intermingled with far too much utter nonsense.
I'm not an expert on many subject areas, but despite my limited exposure to watching it, the number of times I've had to step in and correct something to my parents that GB News has suggested is fact (usually disguised as an opinion) is frightening. They show such a blatant disregard for the truth that I can't take the real issues they raise without a hefty dose of doubt. You certainly can't take many of their guests' opinions at face value, because they're often either being intentionally misleading, or have been misled themselves.
The worst part is, when I point out the misinformation to my parents they don't immediately believe me. Fair enough, so I then go and research it to find out for sure, but then they're not interested to see my research and still believe that almighty GB News couldn't just be lying straight to their faces. It's very scary to see, especially if their viewership is growing nationally.